The FDA said yesterday it would allow some clinical trial patients to resume treatment with Biogen Idec and Elan’s withdrawn multiple sclerosis drug Tysabri. The decision appears to boost the probability of the drug being allowed to return when the FDA decides on the matter, sometime by the end of March. Tysabri was voluntarily withdrawn from the US market by Biogen Idec and Elan last February after two patients developed a rare brain disorder, called progressive multifocal leukoencephalopathy (PML), and one died. In subsequent studies of the drug for Crohn’s disease, a third patient was found to have PML. Even though Tysabri’s return may be imminent, sales of the drug will likely be far lower than before the withdrawal. The drug is also expected to receive a black-box warning, the agency’s strongest kind. “If anything needed a black-box warning, this is one of them,” director of medical policy for the drug division of the FDA, Robert Temple, told The New York Times.